In DNA replication which enzyme makes breaks in the DNA strand to relieve supercoiling?
The correct answer and explanation is:
The enzyme responsible for making breaks in the DNA strand to relieve supercoiling during DNA replication is called topoisomerase. There are two types of topoisomerases involved in this process: topoisomerase I and topoisomerase II.
During DNA replication, as the double helix is unwound by the helicase enzyme to expose the template strands, the molecule tends to become over-supercoiled, particularly ahead of the replication fork. This supercoiling creates tension that can hinder the progression of the replication machinery. Topoisomerase alleviates this issue by introducing temporary breaks in the DNA strand.
Topoisomerase I works by making a single-strand break in the DNA. It then allows the DNA to rotate around the intact strand, relieving the torsional strain caused by the supercoiling. After this, the enzyme re-ligates the broken strand, restoring the DNA structure.
Topoisomerase II, on the other hand, makes double-strand breaks. It works in a more complex manner, introducing a break in both strands of the DNA and passing another section of the DNA through the gap before resealing it. This type of topoisomerase is essential for resolving more severe supercoiling and tangling that can occur during DNA replication.
By reducing the tension in the DNA, topoisomerase ensures that the replication fork can progress smoothly, preventing the DNA from breaking due to excessive twisting. This enzymatic activity is crucial for maintaining the stability of the genome during replication, and inhibitors of topoisomerase are sometimes used in cancer treatment, as they can prevent the replication of cancer cells.